1. Field of the Invention
The present invention relates to aircraft. More particularly, the invention is concerned with aircraft which have a thrust-producing power plant incorporating a propeller which is a so-called ducted propeller (sometimes referred to as a "ducted propulsor"). Ducted propellers can provide a more efficient utilization of engine power at lower air speeds than conventional propeller installations, together with significantly lower tip speeds making them generally quieter in operation.
2. Description of the Prior Art
There have previously been proposed aircraft which comprise a fuselage, a cabin within the fuselage at a forward location, a mainplane, and a ducted propeller carried by the fuselage aft of the cabin. Such a configuration can afford excellent visibility from and convenient access to, the cabin, low cabin noise levels, and a low "ground hazard". However, the designers of all such aircraft known to the present inventor have hitherto chosen to attach the mainplane directly to the fuselage and so to dispose the ducted propeller and the mainplane that the propeller duct is immediately behind or above the wing roots, in some cases the trailing edges of the wing roots actually extending into the upstream end of the duct.
When an aircraft of such a configuration is operated, the air flow through the propeller duct is subject to considerable disturbance from a portion of the turbulent airflow emanating from the mainplane. In fact, tests by the present inventor on such an arrangement have shown that, even at zero angle of incidence of the mainplane, the action of its wake upon the propeller duct flow can be such as to cause severe separation of the flow incident on the propeller from the interior surface of the duct-defining shroud over a significant portion of the circumference thereof. Such separation has the undesirable effect of reducing the propulsive efficiency and increasing the noise generation of the power plant, and it is believed that each of these undesirable effects would be ameliorated if the propeller duct flow were to be freed from the effects of the mainplane wake.